Method and system for migrating a peer in a distributed BGP system

ABSTRACT

A method for peer migration in a distributed Border Gateway Protocol (BGP) system includes: disconnecting a peer relationship between a source BGP process and a network device, wherein first routing information received from the network device is recorded in a forwarding instruction process; establishing a peer relationship between a target BGP process and the network device, and receiving second routing information from the network device; and updating the first routing information recorded in the forwarding instruction process according to the second routing information.

This application claims the priority of Chinese patent application No.200810005295.6, filed Feb. 27, 2008, titled “Method and System forMigrating a Peer in a Distributed BGP System”, the contents of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present disclosure relates to network communication technologies,and in particular, to a method and system for peer migration in adistributed Border Gateway Protocol (BGP) system.

BACKGROUND

With the development of Internet Protocol (IP) technologies, globalInternet users are growing and Internet routes are also growing. Becausenow Internet routes are mainly advertised using the Border GatewayProtocol (BGP), such growth imposes a new challenge to BGP. To tacklethe new challenge, distributed BGP is designed so that BGP neighbor(that is peer) handlings are distributed in different BGP processes andeach BGP process handles only peers related to it. In this way, acentralized handling is changed to a distributed handling.

Two types of BGP processes run on network devices in a distributed BGPsystem: Peer Distributed BGP (PD-BGP) process and Center BGP (C-BGP)process. There may be multiple PD-BGP processes and different PD-BGPprocesses handle different peers.

Because system load is related to the running state of the system (suchas the number of routes, route flapping and policy), some PD-BGPprocesses may be subject to imbalance of loads; or with the growth ofservices, one PD-GBP process may become unable to bear the originalpeers within the BGP process. Both the above situations require thepeers to be migrated from one PD-BGP process to another PD-BGP process,or from a PD-BGP process to a C-BGP process, or from a C-BGP process toa PD-BGP process.

SUMMARY

Embodiments of the present invention provide a method and system forpeer migration in a distributed Border Gateway Protocol (BGP) system,during migration of peers in the distributed BGP system normalforwarding services are not affected.

A method for peer migration in a distributed Border Gateway Protocol(BGP) system includes: disconnecting a peer relationship between asource BGP process and a network device, wherein first routinginformation received from the network device is recorded in a forwardinginstruction process; establishing a peer relationship between a targetBGP process and the network device, and receiving second routinginformation from the network device; and updating the first routinginformation recorded in the forwarding instruction process according tothe second routing information.

A distributed BGP system includes a peer disconnecting unit, a peersetup unit and a route updating unit. The peer disconnecting unit isadapted to disconnect a BGP peer relationship between a source BGPprocess and a network device. The peer setup unit is adapted to set up aBGP peer relationship between a target BGP process and the networkdevice, and receive first routing information from the network device.The route updating unit is adapted to update second routing informationrecorded in a forwarding instruction process which is received from thenetwork device, according to the first routing information received bythe target BGP process from the network device.

A method for peer migration in a distributed BGP system includesnegotiating a graceful restart (GR) function with a network device; andperforming a peer migration for the network device.

A distributed BGP system includes a GR negotiation control unit and apeer migrating unit. The GR negotiation control unit is adapted tonegotiate with a network device to enable a graceful function. The peermigrating unit is adapted to perform a peer migration for the networkdevice.

A computer readable media includes logic encoded in the computerreadable media, the logic when executed is operable to: disconnect apeer relationship between a source BGP process and a network device,wherein first routing information received from the network device isrecorded in a forwarding instruction process; establish a peerrelationship between a target BGP process and the network device, andreceiving second routing information from the network device; and updatethe first routing information recorded in the forwarding instructionprocess according to the second routing information.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 shows an application environment of a distributed BGP systemaccording to an embodiment of the invention;

FIG. 2 is a schematic workflow of the BGP system shown in FIG. 1;

FIG. 3 is a schematic flowchart of the method for peer migration in adistributed BGP system according to an embodiment of the invention;

FIG. 4 gives a specific example illustrating the flowchart of the methodshown in FIG. 3 according to an embodiment of the invention;

FIG. 5 shows a schematic flowchart of the method for peer migration in adistributed BGP system according to an embodiment of the invention;

FIG. 6 shows a schematic flowchart of the method for peer migration in adistributed BGP system according to an embodiment of the invention;

FIG. 7 shows a schematic structure of a distributed BGP system for peermigration according to an embodiment of the invention;

FIG. 8 shows a schematic flowchart of the method for peer migrationaccording to an embodiment of the invention; and

FIG. 9 shows a schematic structure of a distributed BGP system for peermigration according to an embodiment of the invention.

DETAILED DESCRIPTION

As shown in FIG. 1, two types of Border Gateway Protocol (BGP) processesrun in a distributed BGP system: a Peer Distributed BGP (PD-BGP) processand a Center BGP (C-BGP) process. There may be multiple BP-BGP processesin the system while different PD-BGP processes handle different peers.Major functions of a PD-BPG process include:

(1) receiving routing information from peers;

(2) performing an ingress policy filtering;

(3) selecting local optimal routing information and sending the localoptimal routing information to a C-BGP process;

(4) receiving global optimal routing information sent by the C-BGPprocess and sending the global optimal routing information to peers; and

(5) performing an egress policy filtering.

Functionally, the PD-BGP process mainly receives and sends routinginformation and performs a local routing. PD-BGP processes only sendlocal preferred routing information to the C-BGP process so that theC-BGP process only stores routing information that may be preferred.This reduces the usage of memory occupied by the C-BGP process. Inaddition, PD-BGP processes perform the ingress policy filtering and theegress policy filtering, (this may occupy a large part of centralprocessing unit (CPU) resources), and thus reduce the usage of CPU bythe C-BGP process.

Functions of a C-BGP process mainly include:

(1) receiving the local optimal routing information from all PD-BGPprocesses and selecting the global optimal routing information;

(2) generating a forwarding table entry according to the global optimalrouting information to instruct forwarding; and

(3) sending the global optimal routing information to the PD-BGPprocesses so that all the PD-BGP processes can send the global optimalrouting information to the respective peers.

Functionally, the C-BGP process implements all the basic functions ofthe BGP, including the ingress and egress policies for the peers. Inaddition, like a PD-BGP process, the C-BGP process may configure thepeers and further process the configured peers. For example, a firstPD-BGP process processes the peer 1 and peer 2; a second PD-BGP processprocesses the peer 3 and peer 4; and the C-BGP process processes thepeer 5 and peer 6.

The first PD-BGP process receives a message (for example, an Updatemessage) from a peer network device and further receives routinginformation from the peer network device. The first PD-BGP processstores the routing information in a BGP peer ingress routing table(Adj-RIB-IN), the BGP creates one Adj-RIB-IN for each peer. Then thefirst PD-BGP process performs a local routing to get a local optimalroute, and sends the local optimal routing information to the C-BGPprocess. The C-BGP process adds the received local optimal routinginformation to an Adj-RIB-IN and performs a global routing. The C-BGPprocess adds the global optimal routing information to a BGP localrouting table (Loc-RIB). The routing information in the Loc-RIB forms arouting information base (RIB). The C-BGP process sends the globaloptimal routing information in the Loc-RIB to the first PD-BGP processand the PD-BGP process adds the received global optimal routinginformation to its own Loc-RIB. After an egress policy filtering, thefirst PD-BGP process adds the global optimal routing information in theLoc-RIB to a BGP peer egress routing table (Adj-RIB-OUT) which recordsthe routing information sent to the peers, and sends the global optimalrouting information to the corresponding peers.

FIG. 3 shows a flowchart of a method for peer migration in a distributedBGP system according to an embodiment of the invention. In thedistributed BGP system, at least a first PD-BGP process, a second PD-BGPprocess and a C-BGP process are running. Suppose peer 1 (first peernetwork device) is currently managed by the first PD-BGP process and thepeer 1 needs to be migrated, for some specific requirements, to thesecond PD-BGP process. In this embodiment and other embodiments of theinvention, the BGP process managing a peer before migration is definedas a source BGP process and the BGP process managing the peer aftermigration is defined as a target BGP process.

The migration is as follows:

Process 310: Disconnecting the BGP peer relationship between the firstPD-BGP process and the first network device and deleting the routinginformation received from the first network device recorded in the firstPD-BGP process.

Specifically, deleting the configuration information related to peer 1in the first PD-BGP process, disconnecting the BGP peer relationshipbetween the first PD-BGP process and the first network device anddeleting the routing information received from the first network devicein the first PD-BGP process.

Process 320: The first PD-BGP process notifies the C-BGP process thatthe peer 1 is under dynamic migration and the C-BGP process keeps therouting information received from the first network device recorded inthe C-BGP process. In other words, after the BGP peer relationshipbetween the first PD-BGP process and the first network device isdisconnected, the C-BGP still keeps the routing information receivedfrom the first network device.

Specifically, the first PD-BGP process does not notify the C-BGP processto delete the routing information received from the first network devicerecorded in the C-BGP process, but notifies the C-BGP process that thepeer 1 is under dynamic migration. The C-BGP process may record theinformation so as to facilitate the aging processing when the migrationof the peer 1 fails or when a peer relationship is established betweenthe target BGP process (the second PD-BGP process) and the first networkdevice.

Process 330: Establishing a peer relationship between the second PD-BGPprocess and the first network device and receiving routing informationfrom the first network device.

Specifically, the configuration information related to the peer may bere-configured directly in the second PD-BGP process, or may betransferred from the first PD-BGP process to the second PD-BGP processvia a command, for example a compound command. Further, the peerrelationship between the second PD-BGP and the first network device isestablished, the second PD-BGP receives the routing information from thefirst network device, performs a local routing accordingly, and sendsthe local optimal routing information to the C-BGP process.

Process 340: Updating the routing information received from the firstnetwork device recorded in the C-BGP process according to the routinginformation received by the second PD-BGP process from the first networkdevice.

Specifically, the routing information corresponding to the first networkdevice recorded in the C-BGP process is updated according to the routinginformation received by the second PD-BGP process from the first networkdevice, and the routing information that is not updated is deleted. Inother words, if the routing information received from the first networkdevice recorded in the C-BGP process includes the routing informationnot received by the second PD-BGP process from the first network device,the routing information that is recorded in the C-BGP process but is notreceived by the second PD-BGP process is deleted. Thus, this may assurethat the routing information from the first network device recorded inthe C-BGP process is the latest routing information when the peer 1 ismigrated to the second PD-BGP, so as to assure that the serviceforwarding path is correct and, during the migration, a correct responsecan be made to any change in the topology of the peer network device. Inaddition, if the migration of the peer 1 fails, or the migration is notcompleted successfully within a specified time, the routing informationcorresponding to the first network device and recorded in the C-BGPprocess is deleted.

FIG. 4 gives a specific example to illustrate the flowchart of themethod shown in FIG. 3 according to an embodiment of the invention.

A local router A has BGP peer relationships with a peer router B and apeer router C respectively. Three BGP processes are running in therouter A: a C-BGP process, a first PD-BGP process and a second PD-BGPprocess. Now, it is necessary to migrate the BGP peer (peer 1) with therouter C from the first PD-BGP process to the second PD-BGP process onthe router A.

The first PD-BGP process first disconnects the BGP peer relationshipwith the router C, and deletes the routing information (2.2.0.0/16)learnt from the router C, the C-BGP process still keeps the routinginformation so that the router A is not impacted in instructingforwarding services.

For example, during the migration of the peer 1, the packets from therouter B (for example, the packets has a source address 1.1.0.0 and adestination address 2.2.0.0) can still be sent to the router C via therouter D, the router A and the router E and finally sent to thedestination network 2.2.0.0. Since the router A keeps the routinginformation corresponding to the router C that is used to instructforwarding in the C-BGP process, failure of forwarding the packets tothe router C from the router A will not happen because the router A hasthe routing information corresponding to the router C during migration.

Further, before the migration of the peer 1, the router A and the routerC may negotiate to enable the graceful restart (GR) function so thatwhen the BGP peer relationship between the router A and the router C isdisconnected, the router C still keeps the routing informationpreviously learnt from the router A. Thus, the forwarding informationcorresponding to the router A is kept and therefore, data can be sent tothe router A via the router E. This ensures that the forwarding in therouter C is not interrupted.

When the peer 1 is migrated to the second PD-BGP process on the routerA, the second PD-BGP process sets up a peer relationship with the routerC again and receives routing information from the router C. The secondPD-BGP updates the routing information to the C-BGP process so that thesubsequent forwarding path is correct.

FIG. 5 shows a flowchart of a method for peer migration in a distributedBGP system according to an embodiment of the invention. In thisembodiment, peer 1 is migrated to the C-BGP process. The C-BGP processnot only can perform a global routing and instruct forwarding, but alsocan managing the peers like the PD-BGP process.

Process 510: Disconnecting the BGP peer relationship between the firstPD-BGP process and the first network device and deleting the routinginformation received from the first network device recorded in the firstPD-BGP process. The specific implementation is the similar to Process310.

Process 520: The first PD-BGP process notifies the C-BGP process thatthe peer 1 is under dynamic migration, and the C-BGP process keeps therouting information received from the first network device recorded inthe C-BGP process. In other words, after the BGP peer relationshipbetween the first PD-BGP process and the first network device isdisconnected, the C-BGP process still keeps the routing informationreceived from the first network device.

Specifically, the first PD-BGP process does not notify the C-BGP processto delete the routing information which is received from the firstnetwork device and recorded in the C-BGP process, but notifies the C-BGPprocess that the peer 1 is under dynamic migration. Then the C-BGPprocess can record the information so as to facilitate the agingprocessing when the migration of peer 1 fails or when a peerrelationship is set up between the target BGP process (the C-BGPprocess) and the first network device.

Process 530: Establishing a peer relationship between the C-BGP processand the first network device and receiving the routing information fromthe first network device.

Specifically, the configuration information related to the peer 1 may bere-configured directly on the C-BGP process, or may be transferred fromthe first PD-BGP process to the C-BGP process via a command, for examplea compound command. Thus, the peer relationship is established betweenthe C-BGP process and the first network device, and the C-BGP processreceives the routing information from the first network device.

Process 540: Updating the routing information which is received from thefirst network device and recorded in the C-BGP process according to therouting information received by the C-BGP process from the first networkdevice.

Specifically, the routing information corresponding to the first networkdevice and recorded in the C-BGP process is updated according to therouting information received by the C-BGP process from the first networkdevice, and the routing information that is not updated is deleted. Inother words, if the routing information which is received from the firstnetwork device and recorded in the C-BGP process includes the routinginformation not received by the C-BGP process from the first networkdevice, the routing information that is recorded in the C-BGP processbut is not received by the C-BGP process is deleted. Then, the C-BGPprocess performs a normal global route selection to get a latest globaloptimal route so as to ensure that the latest routing information of thefirst network device is recorded in the C-BGP process after peer 1 ismigrated to the C-BGP process and that the service forwarding path iscorrect. In addition, a correct response can be made to any change inthe topology of the peer network device.

In addition, if the migration of the peer 1 fails, or the migration isnot completed successfully within a specified time, the routinginformation which is received from the first network device and recordedin the C-BGP process is deleted.

FIG. 6 shows a flowchart of the method for peer migration in adistributed BGP system according to an embodiment of the invention. Inthis embodiment, the peer 1 is migrated from a C-BGP process to a firstPD-BGP process. The C-BGP process not only can perform a global routingand instruct forwarding, but also handle the peers like a PD-BGPprocess.

Process 610: Disconnecting the BGP peer relationship between the C-BGPprocess and the first network device and keeping the routing informationreceived from the first network device recorded in the C-BGP process. Inother words, after the BGP peer relationship between the C-BGP processand the first network device is disconnected, the C-BGP process stillkeeps the routing information received from the first network device.

Specifically, deleting the configuration information related to the peer1 in the C-BGP process, disconnecting the BGP peer relationship with thefirst network device and keeping the routing information received fromthe first network device recorded in the C-BGP. In addition, the C-BGPprocess may also record that the peer 1 is under dynamic migration.

Process 620: Establishing a BGP peer relationship between the firstPD-BGP process and the first network device and receiving routinginformation from the first network device.

Specifically, the configuration information related to peer 1 may bere-configured directly on the first PD-BGP process, or may betransferred from the C-BGP process to the first PD-BGP process via acommand, for example a compound command. Further, the first PD-BGPprocess establishes the BGP peer relationship with the first networkdevice, receives the routing information from the first network device,performs a local routing accordingly, and sends the local optimalrouting information to the C-BGP process.

Process 630: Updating the routing information which is received from thefirst network device and recorded in the C-BGP process according to therouting information received by the first PD-BGP process from the firstnetwork device.

In addition, if the migration of the peer 1 fails, or the migration isnot completed successfully within a specified time, the routinginformation corresponding to the first network device recorded in theC-BGP process is deleted.

FIG. 7 shows a schematic structure of a distributed BGP system for peermigration according to an embodiment of the invention. The distributedBGP system includes a peer disconnecting unit 71, a recording unit 72, apeer setup unit 73 and a route updating unit 74.

The peer disconnecting unit 71 is adapted to disconnect the BGP peerrelationship between the source BGP process and the peer network device;the recording unit 72 is adapted to record the routing informationreceived from the peer network device in the C-BGP process and keep therecord after the BGP peer relationship between the source BGP processand the peer network device is disconnected; the peer setup unit 73 isadapted to establish a BGP peer relationship between the target BGPprocess and the peer network device and receive routing information fromthe peer network device; the route updating unit 74 is adapted to updatethe routing information which is received from the peer network deviceand recorded in the C-BGP process according to the routing informationreceived by the target BGP process from the peer network device.

The route updating unit 74 may further include an aging unit 742. Theaging unit 742 is adapted to delete the routing information that isrecorded in the C-BGP process but is not received by the target BGPprocess when the routing information which is received from the firstnetwork device and recorded in the C-BGP process includes the routinginformation not received by the target BGP process from the firstnetwork device. The route updating unit 74 is designed to ensure theconsistency between the routing information corresponding to the peernetwork device and recorded in the C-BGP process and the routinginformation received by the target BGP process from the peer networkdevice after the peer migration, and further ensure the correctness ofthe forwarding path and the correct response to any change in thetopology in the peer network during the migration.

The distributed BGP system may further include a GR negotiation controlunit, adapted to negotiate with the peer network device to enable the GRfunction before the peer migration. Due to the existence of the GRnegotiation control unit, the forwarding service on the peer networkdevice is not impacted during the peer migration.

Because there are different means of peer migration, the source BGPprocess in the embodiments of the invention may be a first PD-BGPprocess and the target BGP process is a second PD-BGP process; or thesource BGP process is a first PD-BGP process and the target BGP processis a C-BGP process; or the source BGP process is a C-BGP process and thetarget BGP process is a first PD-BGP process.

When the source BGP process is a first PD-BGP process, the distributedBGP system may further include a first deleting unit, adapted to deletethe routing information corresponding to the peer network devicerecorded in the first PD-BGP process after the BGP peer relationshipbetween the first PD-BGP process and the peer network device isdisconnected; and a migration notifying unit, adapted to notify theC-BGP process that the peer network device is under dynamic migrationafter the BGP peer relationship between the first PD-BGP process and thepeer network device is disconnected. When the source BGP process is aC-BGP process, the distributed BGP system may not include the abovefirst deleting unit and the migration notifying unit.

It is understood that the distributed BGP system in the aboveembodiments of the invention may be a specific network device, forexample a router or a layer-3 switch etc. In addition, because the majorfunction of the C-BGP process is to collect routing information receivedby all the PD-BP processes to instruct forwarding, a special process maybe included in a distributed BGP system to provide the forwardinginstruction function of the C-BGP process. Therefore, the above specialprocess and the C-BGP process may be called together a forwardinginstruction process. Accordingly, the technical scheme implemented inthe C-BGP process in the above embodiments of the invention, for examplekeeping the routing information received from the peer network devicerecorded in the C-BGP process during the peer migration and updating therouting information etc., may be implemented in the forwardinginstruction process.

The routing information recorded in the forwarding instruction processis adapted to instruct service forwarding. During the peer migration,the routing information which is received from the peer network deviceand recorded in the forwarding instruction process of the distributedBGP system is kept and the routing information recorded in theforwarding instruction process is updated according to the routinginformation received by the target BGP process after the migration. As aresult, the service forwarding of the distributed BGP system is notimpacted during the migration.

In addition, because the GR function is enabled for the peer networkdevice, the peer network device keeps the routing information previouslyrecorded after the peer relationship with the peer network device isdisconnected during the migration. Therefore, the service forwarding onthe peer network device is not impacted during the peer migrationprocess.

FIG. 8 shows a flowchart of the method for peer migration in adistributed BGP system according to an embodiment of the invention.

Process 810: Negotiating with the peer network device to enable the GRfunction.

Process 820: Migrating the peer after the GR function is enabled.

The peer migration may follow the technical scheme implemented in theabove embodiments of the invention.

In addition, the technical scheme below may be followed:

Disconnect the BGP peer relationship between the source BGP process andthe peer network device and delete the routing information received fromthe peer network device recorded in the forwarding instruction process;set up a BGP peer relationship between the target BGP process and thepeer network device and receive routing information from the peernetwork device; and send the routing information received by the targetBGP process from the peer network device to the forwarding instructionprocess.

Though the routing information received from the peer network devicerecorded in the forwarding instruction process is not kept during thepeer migration, because the GR function is enabled in Process 810, whenthe local network device (a second network device) migrates its peerrelationship with the peer network device (a first network device), forexample the second network device disconnects the peer relationship withthe first network device, the second network device keeps thepreviously-recorded routing information received from the first networkdevice. As a result, the service forwarding on the first network deviceis not affected by the peer migration.

FIG. 9 shows a schematic structure of a distributed BGP system for peermigration according to an embodiment of the invention. The distributedBGP system in this embodiment includes a GR negotiation control unit 91and a peer migrating unit 92.

The GR negotiation control unit 91 is adapted to negotiate with the peernetwork device to enable the GR function before peer migration.

The peer migrating unit 92 may be implemented in various ways, forexample, the structure shown in FIG. 7.

The peer migrating unit 92 may also adopt the following structure: thepeer migrating unit includes: a peer disconnecting unit, adapted todisconnect the BGP peer relationship between the source BGP process andthe peer network device; a second deleting unit, adapted to delete therouting information received from the peer network device when the BGPpeer relationship between the source BGP process and the peer networkdevice is disconnected; a peer setup unit, adapted to set up a BGPrelation between the target BGP process and the peer network device andreceive routing information from the peer network device; and a routeproviding unit, adapted to provide the routing information received bythe target BGP process from the peer network device for the forwardinginstruction process.

In the above implementation of the peer migrating unit 92, the routinginformation received from the peer network device recorded in theforwarding instruction process is not kept during peer migration, butbecause the peer migrating unit 92 migrates the peer after the GRnegotiation control unit 91 negotiates with the peer network device toenable the GR function, the service forwarding on the peer networkdevice is not impacted during the peer migration.

In an embodiment, computer readable media comprises computer programcodes for migrating peer in a distributed BGP system. The computerprogram codes may be logic encoded in one or more tangible media forexecution. As used herein, logic encoded in one or more tangible mediais defined as instructions that are executable by a programmed processorand that are provided on computer-readable storage media, memories, or acombination thereof. When executed, the logic is operable to disconnecta peer relationship between a source BGP process and a network device,wherein first routing information received from the network device isrecorded in a forwarding instruction process; establish a peerrelationship between a target BGP process and the network device, andreceiving second routing information from the network device; and updatethe first routing information recorded in the forwarding instructionprocess according to the second routing information. When executed, thelogic encoded in one or more tangible media is also operable tonegotiate a graceful restart (GR) function with a network device; andperform a peer migration for the network device.

Although the invention has been described through exemplary embodiments,the invention is not limited to such embodiments. It is apparent thatthose skilled in the art can make various modifications and variationsto the invention without departing from the spirit and scope of theinvention. The invention is intended to cover the modifications andvariations provided that they fall in the scope of protection defined bythe claims or their equivalents.

1. A method for peer migration in a distributed Border Gateway Protocol(BGP) system, comprising: disconnecting a peer relationship between asource BGP process and a network device, wherein first routinginformation received from the network device is recorded in a forwardinginstruction process; establishing a peer relationship between a targetBGP process and the network device, and receiving second routinginformation from the network device; updating the first routinginformation recorded in the forwarding instruction process according tothe second routing information.
 2. The method according to claim 1,wherein the updating process comprises: deleting routing information notreceived by the target BGP process from the first routing informationrecorded in the forwarding instruction process if the first routinginformation comprises the routing information not received by the targetprocess.
 3. The method according to claim 1, before the disconnectingprocess, the method further comprising: negotiating with the networkdevice to enable a graceful restart (GR) function.
 4. The methodaccording to claim 1, wherein the source BGP process is a first PeerDistributed BGP (PD-BGP) process and the target BGP process is a secondPD-BGP process; or the source BGP process is a first Peer DistributedBGP (PD-BGP) process and the target BGP process is a center BGP (C-BGP)process; or the source BGP process is a C-BGP process and the target BGPprocess is a first PD-BGP process.
 5. The method according to claim 1,comprising: deleting routing information recorded in the source BGPprocess which is received from the network device after disconnectingthe BGP peer relationship between the source BGP process and the networkdevice.
 6. The method according to claim 1, comprising: notifying, bythe source BGP process, the forwarding instruction process that thenetwork device is under dynamic migration.
 7. A distributed BorderGateway Protocol (BGP) system, comprising: a peer disconnecting unit,configured to disconnect a BGP peer relationship between a source BGPprocess and a network device; a peer setup unit, configured to set up aBGP peer relationship between a target BGP process and the networkdevice, and receive first routing information from the network device;and a route updating unit, configured to update second routinginformation recorded in a forwarding instruction process which isreceived from the network device, according to the first routinginformation received by the target BGP process from the network device.8. The system according to claim 7, wherein the route updating unitcomprises an aging unit configured to delete routing information notreceived by the target BGP process from the second routing informationrecorded in the forwarding instruction process, if the second routinginformation recorded in the forwarding instruction process comprises therouting information not received by the target BGP process from thenetwork device.
 9. The system according to claim 7, further comprising:a deleting unit configured to delete routing information recorded in thesource BGP process which is received from the network device afterdisconnecting the BGP peer relationship between the source BGP processand the network device.
 10. The system according to claim 7, furthercomprising: a migration notifying unit configured to notify theforwarding instruction process that the network device is under dynamicmigration after disconnecting the BGP peer relation between the sourceBGP process and the network device.
 11. The system according to claim 7,further comprising a graceful restart (GR) negotiation control unit,configured to negotiate with the network device to enable a GR functionafter the BGP peer relationship between the source BGP process and thenetwork device is disconnected.
 12. A method for peer migration in adistributed Border Gateway Protocol (BGP) system, comprising:negotiating a graceful restart (GR) function with a network device; andperforming a peer migration for the network device, wherein performingthe peer migration for the network device comprises: disconnecting a BGPpeer relationship between a source BGP process and the network device,and deleting first routing information recorded in a forwardinginstruction process which is received from the network device;establishing a BGP peer relationship between a target BGP process andthe network device, and receiving second routing information from thenetwork device; and providing the second routing information to theforwarding instruction process.
 13. A distributed Border GatewayProtocol (BGP) system, comprising: a GR negotiation control unit,configured to negotiate with a network device to enable a gracefulfunction; and a peer migrating unit, configured to perform a peermigration for the network device, wherein the peer migration unitcomprises: a peer disconnecting unit, configured to disconnect a BGPpeer relationship between a source BGP process and the network device; adeleting unit, configured to delete first routing information recordedin a forwarding instruction process which is received from the networkdevice; a peer setup unit, configured to establish a BGP peerrelationship between a target BGP process and the network device, andreceive second routing information from the network device; and a routeproviding unit, configured to provide the second routing information tothe forwarding instruction process.
 14. A non-transitory computerreadable media, comprising logic encoded in the computer readable media,the logic when executed operable to: disconnect a peer relationshipbetween a source BGP process and a network device, wherein first routinginformation received from the network device is recorded in a forwardinginstruction process; establish a peer relationship between a target BGPprocess and the network device, and receiving second routing informationfrom the network device; and update the first routing informationrecorded in the forwarding instruction process according to the secondrouting information.